The Vermont Department of Health has alerted health care providers across the state about a rising number of cases of pertussis, better known as whooping cough.

State health officials said Wednesday that nine cases of pertussis have been confirmed in Vermont, including five in the past two weeks alone. Pertussis is a highly contagious disease of the lungs caused by a bacterial infection.

No cases have been confirmed in southern Vermont, according to Southwestern Vermont Medical Center and state health officials, but it is possible undiagnosed cases exist and health care providers have been alerted.

Vermont Health Commissioner Wendy Davis said whooping cough is somewhat common for the season, but should be taken seriously.

"The number of cases of pertussis is not unusually high for this time of year, but it is a good reminder for parents, providers and school health officials to make sure children are fully vaccinated, and to look for symptoms of the disease," Davis said. "Teenagers and adults should also check their records, since they are a frequent source of exposure to infection for infants and young children."